A reluctance motor with a fixed armature having a magnetic pole wound repeatedly with armature coils of plural phases will be explained hereinafter with respect to current supply to the armature coils. In the following explanation, angles without any special comments are electric angles.
Furthermore, in the following description, the terms "one direction" may be replaced with the terms "forward direction" or "going direction", while the term "the other direction" may be replaced with the term "reverse direction" or "returning direction".
FIG. 1 is a cross-sectional view showing a fixed armature and a rotor. Rotors 1, each formed by laminating electromagnetic steel sheets, are equipped with salient poles 1a, 1b, each having a width of 180 degrees (=90 degrees in terms of mechanical angle), and are mutually spaced with a phase difference of 360 degrees. A rotational shaft 2 is provided at a center of the rotor 1. The arrow A indicates a rotational direction of the rotor 1.
A fixed armature 3, similarly formed by laminating electromagnetic steel sheets, has an inside surface provided with twelve uniformly spaced slots 3a, 3b, 3c, - - - , and is fixed to a frame member 4.
The slots 3a, 3d are respectively wound with one coil, while the slots 3g, 3j are respectively wound with another coil. To constitute a 1st-phase armature coil, these two coils are connected with each other in series or in parallel, although they are connected in series in this embodiment.
The slots 3b, 3e be are wound with one coil, while the slots 3h, 3k are wound with another coil. These two coils are connected with each other in series, thus constituting a 2nd-phase armature coil.
The slots 3c, 3f are wound with one coil, while the slots 3i, 3l are wound with another coil. These two coils are connected with each other in series, thus constituting a 3rd-phase armature coil.
FIG. 2 is an embodiment showing the rotor 1, a rotational plate 15 detecting the position of rotor 1, and armature coils.
In FIG. 2, armature coils 5a and 5d represent the previously-described 1st-phase armature coil. Armature coils 5b and 5e represent the previously-described 2nd-phase armature coil. Armature coils 5c and 5f represent the previously-described 3rd-phase armature coil. Lead terminals of 1st-, 2nd- and 3rd-phase armature coils are denoted by reference numerals 6a, 6b and 6c, 6d and 6e, 6f, respectively.
The above-described 1st-, 2nd- and 3rd-phase armature coils 5a, 5d and 5b, 5e and 5c, 5f are referred to as armature coils 7a, 7b and 7c, respectively, hereinafter.
Next, an explanation will be made as to the case where the above-described armature coils 7a, 7b and 7c are respectively supplied with electric current through a well-known current supply control circuit which has switching elements at the side of the positive pole as well as at the side of the negative pole of the armature coil, and designed to supply the current flowing in one direction, from the side of the positive pole to the side of negative pole of the armature coil.
In FIGS. 1 and 2, when the armature coil 7b is activated, the salient poles 1a and 1b are magnetically attracted, causing the rotor 1 to rotate in a direction of the arrow A. When the rotor 1 rotates 90 degrees, the armature coil 7b is deactivated, and the armature coil 7c is activated. When the rotor 1 further rotates 120 degrees, the armature coil 7c is deactivated, and the armature coil 7a is activated. A current supply mode is cyclically alternated in every 120-degree rotation in order of armature coil 7a.fwdarw.armature coil 7b.fwdarw.armature coil 7c. That is, the armature coils are supplied with electric current in order of 1st-phase.fwdarw.2rd-phase.fwdarw.3rd phase. Repetition of such a current supply mode enables a motor to be driven as a three-phase half-wave motor.
As indicated by the current supply curves 8a, 8b and 8c of the respective armature coils shown in FIG. 17, the supply of current starts at 0 degrees of overlapping between the salient pole of the rotor and the magnetic pole of the armature, and the current in the armature coil decreases rapidly when the supply of current is discontinued at 120 degrees of overlapping, but the current caused by the inductance flows as indicated by curves 9a, 9b and 9c even where exceeding 120 degrees of overlapping.
According to the one-way current supply to the armature coils of FIGS. 1 and 2, magnetization of N- and S-poles due to current supply to respective armature coils is repeated in the order of FIG. 3.fwdarw.FIG. 4.fwdarw.FIG. 5.fwdarw.FIG. 3.fwdarw.FIG. 4.fwdarw.FIG. 5, - - - . However, when the magnetization of FIG. 5 is changed to that of FIG. 3, that is, when the current supply of the 3rd phase is changed to that of the 1st phase, for the magnetic pole 3A where the 3rd phase armature coil 7c wound in slots 3e, 3h and 3k, 3b and the 1st phase armature coil 7a wound in slots 3a, 3d and 3g, 3j are wound together, in FIG. 1, the N-pole magnetization of FIG. 3 according to current curve 8a of the 1st phase current supply occurs simultaneously with S-pole magnetization of FIG. 5 according to current curve 9c of the inductance at the time of the 3rd phase current supply discontinuation. Further, for the magnetic pole 3G, S-pole magnetization of FIG. 3 according to current curve 8a of the 1st phase current supply occurs simultaneously with N-pole magnetization of FIG. 5 according to current curve 9c of the inductance at the time of the 3rd phase current supply discontinuation. Such current supply to an armature coil may cause drawbacks such as reduction of the rotational torque, drop of output and operation efficiency and occurrence of vibration and noise.
For this reason, the magnetization system is arranged so that the magnetization of N- and S-poles by current supplied to respective armature coils takes place in the order of FIG. 3.fwdarw.FIG. 4.fwdarw.FIG. 5.fwdarw.FIG. 6.fwdarw.FIG. 7.fwdarw.FIG. 8, so as to cause a rotational magnetization.
To realize the magnetization in the cases illustrated in FIGS. 3, 4 and 5 and the magnetization in the cases illustrated in FIGS. 6, 7 and 8, direction of current supplied to the armature coils needs to be changed in a reciprocative manner.
According to one conventional current supply control circuit for changing direction of current to be supplied to armature coils in a reciprocative manner, one end and the other end of each armature coil are connected with each other to constitute a circular connection, and there are provided switching elements at positive and negative terminal sides of a power source in the above connecting points to constitute a bridge circuit respectively.
This circuit can change the direction of current flowing through the armature coil of one phase from a going direction to a returning direction, i.e. from one direction to the other direction, and vice versa; however, this circuit is not applicable to reluctance motors because the current also flows through another armature coil of the other phase simultaneously to cause counter torque.
In the reluctance motors, a current supply to an armature coil of each phase needs to be made in a limited period divided according to the number of phases. To accomplish this end, one well known current supply control circuit comprises a bridge circuit formed by providing switching elements at the positive terminal side and negative terminal side of a power source in one end and the other end of each armature coil.
This circuit is designed to activate respective phase armature coils 7a, 7b and 7c to cause the rotational magnetization of N- and S-poles to occur in the order of FIG. 3.fwdarw.FIG. 4.fwdarw.FIG. 5.fwdarw.FIG. 6.fwdarw.FIG. 7.fwdarw.FIG. 8, but the following disadvantages are involved.
The conventional current supply control of the reluctance motor is required to comprise at least four times as many expensive switching elements for reciprocating activation of the armature coils as the number of the phase, and this entails the disadvantages such as complex composition, high cost, large dimensions and weight of the circuit.
Thus, an object of the present invention is to provide a current supply control circuit for reluctance motors which contributes to improving the efficiency of reluctance motors, as well as to suppressing noise and vibration, and to the reduction of price, size and weight of the circuit.